Y. pestis, the etiologic agent of plague, was introduced into the United States at the turn of the 20th century; therefore, the genetic and phenotypic diversity of American Y. pestis isolates is relatively limited. In contrast, Y. pestis has been endemic in many countries of the former Soviet Union (FSU) for many centuries and numerous Y. pestis-related publications in the FSU's literature strongly suggest that the FSU's Y. pestis strains are genetically more diverse than are American Y. pestis isolates. Understanding the genetic and virulence trait differences among strains will be of critical importance during the development of advanced tools and strategies to deal with possible Y. pestis-related bioterrorism attacks in the USA and elsewhere. Therefore, we propose to begin a comprehensive characterization of Y. pestis strains from several endemic loci of plague in the FSU's Caucasus region, and to begin delineating the critical differences between the genetic make-up and virulence traits of Y. pestis strains from the FSU and elsewhere. Three specific aims will be addressed: (1) Characterize the genomic variability of Y. pestis strains from the FSU, and perform comparative MLST, PFGE, and MLVA analyses for Y. pestis fingerprinting, (2) Characterize the plasmid compositions of the FSU's Y. pestis isolates, and perform nucleotide sequence-based analyses of selected plasmid- and chromosomally-encoded virulence genes, and (3) Begin elucidating the prevalence and the expression patterns of major virulence genes in the FSU's Y. pestis isolates, using microarrays and RT PCR The R21 grant mechanism is ideally suited for supporting our proposed studies, and it will help us to generate important information/initial data concerning the genetic make-up and gene expression patterns of Y. pestis isolates previously unavailable to investigators outside the FSU, and for which very little information is currently available. The generated data will also play a critical role in our designing appropriate future studies, and in expanding our Y. pestis research program at the University of Maryland School of Medicine.